As things get further away, from us, they seems smaller and closer together. When they get far enough away, distances become ever tinier and so form a single point. In one-point perspective, all the horizontal lines go straight across, while the lines that move away from us - the sides of boxes, the road we are on, or the railway lines in front of us - all converge towards the center of the picture.
In two-point perspective, our subject is angled so that the two sides, left and right, each have their own vanishing point. In real life, the angle between these combines with our low point of view to make the vanishing points very far apart. If you're drawing from life and try to contstruct your vanishing points, you'll find that they are often right off the paper, sometimes as much as a whole yard or meter across your wall or table! When working from a photograph, that distance can change depending on the lens used by the photographer. When you are constructing perspective, you can put your vanishing points on the edges of your paper, or attach an extra sheet to the sides of your page while working, to create a more natural angle.